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981.
982.
The order of reactivity of OH and NH groups of glucosamine hydrochloride (GlcNH2.HCl) and N-acetyl glucosamine (GlcNAc) toward benzylation with NaH/BnBr in DMF was investigated. For GlcNH2.HCl, benzyl groups were introduced in the order of N-Bn > N-Bn2 > 1-O-Bn > 6-O-Bn > 4-O-Bn > 3-O-Bn; for GlcNAc, benzyl groups were introduced in the order of 1-O-Bn > 6-O-Bn > 4-O-Bn > 3-O-Bn > N-Bn. A range of partially benzylated 2-N,N′-dibenzyl glucopyranosides and GlcNAc derivatives were obtained in a single step.  相似文献   
983.
984.
In this work, a powerful analytical method, called Liao’s homotopy analysis method is used to study the limit cycle of a two-dimensional nonlinear dynamical system, namely the van der Pol oscillator with delayed amplitude limiting. It is shown that the solutions are valid for a wide range of variation of the system parameters. Comparison of the obtained solutions with those achieved by numerical solutions and by other perturbation techniques shows that the utilized method is effective and convenient to solve this type of problems with the desired order of approximation.  相似文献   
985.
Preyssler-type heteropoly acid is introduced as a new,mild and efficient catalyst for protection of a variety of carbonyl compounds with 1,3-propane dithiol.  相似文献   
986.
Double Heck cross‐coupling reactions of 2,3‐ and 3,5‐dibromopyridine with various alkenes afforded the corresponding novel di(alkenyl)pyridines. The Heck reaction of 2,5‐dibromopyridine unexpectedly afforded 5,5′‐di(alkenyl)‐2,2′‐bipyridines by palladium‐catalyzed dimerization to give 5,5′‐dibromo‐2,2′‐bipyridine and subsequent twofold Heck reaction.  相似文献   
987.
Influences of Different Enzymatic Treatment on Denim Garment   总被引:1,自引:0,他引:1  
In current study, the effects of different enzymatic treatment including acid cellulases, neutral cellulases, and combination of laccases with cellulases on denim garment were investigated. The color changes of different samples were compared by colorimetric indices for the garment surface and back and also white pocket. Abrasion resistance, tensile strength, and crease recovery angle of the samples were measured within the standard methods. Also, surfaces of the treated samples were observed by SEM. The results showed that the combination of laccases with cellulases help to improve the lightness and decrease staining on both back of garment and on white pocket.  相似文献   
988.
The ordinary generalized geometric–arithmetic index of graphs is introduced and some properties especially lower and upper bounds in terms of other graph invariants and topological indices are obtained.  相似文献   
989.
990.
The aminocarbonylation and alkoxycarbonylation reactions of terminal alkynes took place smoothly and efficiently using a catalyst system Pd(OAc)2–dppb–p‐TsOH? CH3CN? CO under relatively mild experimental conditions. The catalytic system was tested and optimized using two different nucleophiles: alcohols and amines. Phenylacetylene (1a) was considered as an alkyne along with diisobutylamine (2b1) and methanol (2c1) as nucleophiles. The results showed significant differences in the conversion of 1a and in the selectivity towards the gem or trans unsaturated esters or amides with these nucleophiles. The effects of the type of palladium catalysts, the type of ligands, the amount of dppb and the solvents were carefully studied. With diisobutylamine (2b1), excellent regioselectivity towards the 2‐acrylamides (gem isomer, 3ab1) was almost always observed, while trans‐α,β‐unsaturated esters 4ac1 was the predominant product with methanol (2c1) as a nucleophile. This remarkable sensitivity in the selectivity of the reaction indicates two different possible mechanistic pathways for these carbonylation reactions. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
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